Finite element simulation of nano-filaments pull-out from cementitious nanocomposite materials using an elastic-plastic-damage and cohesive surface models

The main focus of this work is on investigating computationally the pull-out behavior of nano-filaments from the cement matrix. The effects of: (1) nano-filament-cement interfacial shear strength, stiffness, and fracture energy; (2) the mechanical properties of the cement; and (3) nano-filament mechanical properties, aspect ratio, and surface area to volume ratio on the pull-out strength from a cement matrix are investigated through simulating the nano-filament pull-out. A coupled elastic-plastic-damage constitutive model is adopted to simulate the behavior of the cement matrix, whereas the continuum shell model is used to simulate the elastic behavior of the nano-filament. The surface-based cohesive behavior is employed for modeling the interface between nano-filament and cement matrix. It is shown that the nano-filament pull-out force is mainly governed by the interfacial fracture energy, and not the interfacial shear strength. It is also shown that the pull-out strength and damage evolution in the cement matrix during the pull-out process are independent of the nano-filament embedded length, while the final debonding displacement is increased with the increase of the embedded length. Finally, it is shown that the Young's modulus and surface area to volume ratio of the nano-filament are other important key parameters that alters the pull-out strength.